Browsing by Author "Guzman, Diego"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    CdTe quantum dots modified electrodes ITO-(Polycation/QDs) for carbon dioxide reduction to methanol
    (ELSEVIER, 2020) Guzman, Diego; Isaacs, Mauricio; Tsukuda, Tatsuya; Yamazoe, Seiji; Takahata, Ryo; Schrebler, Ricardo; Burgos, Ana; Osorio Roman, Igor; Castillo, Francisco
    The present work describes the characterization by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and electrochemical techniques of ITO modified electrodes with electrostatic assemblies (Polycation/Quantum Dots) and their use in the electro- and photoelectrocatalytic reduction of CO2. These assemblies were prepared with polycations poly-diallyldimethylammonium (PD) and poly-(2-trimethylammonium) ethyl methacrylate (PM) and nanocrystals of CdTe of 2.77 nm (Q2). The size of the nanocrystals was controlled by the synthesis reflux time and incorporated by electric field directed Layer-by-Layer assembly method (EFDLA). The polycations were characterised by NMR measurements; showing important effects on the electrostatic assemblies. PM modified electrodes, with its lower rigidity, exhibited less roughness than the PD modified electrodes, 8.0 nm versus 32.8 nm, and higher heterogeneity in its surface composition. Higher resistance to the charge transfer and time constants were obtained with PMQ2 modified electrode, 63.8 Omega cm(-2) and 2.69 ms versus 49.30 Omega cm(-2) and 1.3 ms for PDQ2. The electro- and photoelectro properties for CO 2 reduction were studied through j-E curves and potential controlled electrolysis. Modified surfaces were active toward the reduction of CO2, with a positive shift of the activity between darkness and irradiation conditions, 0.050 V with PDQ2 and 0.450 V with PMQ2. The main product of the CO2 reduction was CH3OH, with traces of CO and HCOOH. The PM modified electrodes with QDs of 2.77 nm presented a selective behaviour for the production of CH3OH.
  • No Thumbnail Available
    Item
    Hydrogen Productivity Analysis Using Low Concentration of TiO2-Au Nanoparticles on a Ultraviolet-LED-Based Photocatalytic Reactors
    (2021) Varas Concha, Felipe; Guzman, Diego; Isaacs, Mauricio; Saez Navarrete, Cesar
    The productivity of photocatalytic hydrogen generation via photo-reforming of organic compounds has not been studied under low concentrations of catalyst, which could lead to relevant cost savings in future real-scale applications. Herein, it uses half of the lowest concentration of nanoparticles reported of modified P25 TiO2 partially coated with gold. The nanomaterial is prepared using a non-energy intensive, chemical reduction method. Gold content on the TiO2 surface is reported (14%-surface; 9.1%-weight). Dynamic light scattering and transmission electron microscope image analyses show low agglomeration and non-homogeneous shape. Aggregates and gold nanoparticles reach average diameters of 92 and 3.8 nm, respectively. Photocatalytic experiments for hydrogen production are carried out at low concentration of nanoparticles (0.056 g L-1) in methanol-water solution (5%vol.) under 375 nm UV and visible light (20 mW cm(-2)). The system shows a catalyst productivity of 6661 mu mol h(-1) g(-1), a third of the highest reported productivity using methanol (which used a catalyst concentration 18x higher, an alcohol concentration 5x higher, and 100% anatase). The system shows an estimated reaction rate of 373 mu mol L-1 h(-1) with an apparent zero order kinetic, an overall energy conversion efficiency of 0.47%, and an apparent quantum yield of 1.03%.